Apparatuses for cooling articles are commonly known in the art. A cooling channel for articles being covered with a chocolate mass and the like is known from German Patent No. 196 07 055 C2. The articles are located on a conveyor belt, and they are transported thereon through the cooling channel. The cooling channel includes two cooling stretches in which three cooling zones are formed. Air is used as cooling medium. The air being cooled by an evaporating apparatus is introduced approximately in the middle region of the cooling channel at an entering temperature for each cooling stretch. Both cooling stretches are separated by a bottom plate. The cooling medium of the first cooling stretch streams in an inverse direction, first above the bottom plate (radiation cooling), and then below the bottom plate (convection cooling) in the direction toward the entrance of the cooling channel. Its direction is changed there such that it is guided back in the same direction as the articles toward the middle region of the cooling channel. Convection cooling at a parallel flow prevails in the second cooling stretch approximately thermally treating the middle region to the exit of the cooling channel. Thus, the articles are carefully cooled in the middle region of the cooling channel. The articles are intensively cooled in the second cooling stretch. Consequently, there is a temperature profile along the length of the cooling channel. The temperature profile consists of locally different temperatures of the cooling medium by which heat is withdrawn from the articles. The curve illustrating the decreasing temperature of the articles attainable with the temperature profile substantially corresponds to the curve illustrating the solidification of the chocolate mass on the articles.
During a constant load of the cooling channel, meaning when a constant number of articles per unit of time passes the cooling channel, there is a temperature profile extending along the length of the cooling channel that corresponds to the solidifying condition. The cooling channel fulfils its cooling function. This means that the cooling medium enters each cooling stretch in the middle region of the cooling channel at a correspondingly low entering temperature, it absorbs heat from the articles, and it leaves the cooling stretch of the cooling channel at a correspondingly increased exiting temperature. Consequently, the entering temperature of the cooling medium in the middle region of the cooling channel has to be kept at a lower value than the exiting temperature to attain a constant cooling effect for the articles. In case of changing loads of the cooling channel, there is the necessity of changing and adapting, respectively, the cooling effect. This is especially the case when the production is stopped, and the production is newly started afterwards.
A method of cooling covered food, especially sweets and bakery products, is known from German Patent Application No. 197 24 639 A1. The articles are conveyed through the cooling channel on a conveyor belt. There are two cooling circuits and two cooling stretches, the cooling medium approximately entering the cooling channel in the middle region of the cooling channel. A liquid cooling medium is used for the bottom cooling (contact cooling). The upper cooling of the articles (convection cooling) is realized by air as cooling medium. This is effected in the first cooling stretch in an inverse flow, and in the second cooling stretch with a flow in the direction of the movement of the articles. The method is possibly based on a certain entering temperature (flow temperature) of the cooling medium, the temperature either being determined in response to the prevailing conditions, or being constant. The streaming velocity of the cooling medium is being controlled. The streaming velocity is changed in a way such that there is a temperature difference between the exiting temperature and the entering temperature of the cooling medium with which the product is produced with the desired quality. The lower the streaming velocity of the cooling medium is, the greater is the temperature difference. The velocity of the cooling medium is changed by a frequency control allowing for a limited range of control. The control of the velocity of the cooling medium corresponds to the control of the amount of the cooling medium. In this way, it is possible to realize an adaptation to changing conditions. On the other hand, the streaming conditions in the corresponding cooling stretch are changed when the velocity of the cooling medium is changed. This means that the articles are differently treated along the width of the cooling channel at different loads. The articles are differently thermally treated. When the temperature difference during the production of the product at the desired quality has been determined, the value of the temperature difference is entered as the desired value for the production in a way that it is determined for the further cooling process of the product. All this may happen during a full load of the cooling channel. When the production is stopped the entering temperature of the cooling medium is controlled in a way that the actual value of the exiting temperature of the cooling medium is determined and the desired value is changed corresponding to the actual value of the temperature difference. The entering temperature of the cooling medium is raised up to a value below the exiting temperature at a small temperature difference. In this way, the correct exiting temperature of the cooling medium is to be attained when the products enter the cooling channel. In case of a longer stop of the production, meaning that no articles enter the cooling channel, there is the danger of the desired temperature difference between the exiting temperature and the entering temperature of the cooling medium not being kept constant. Since no articles enter the cooling channel, and no articles transfer heat, the exiting temperature of the cooling medium will decrease to the value of the entering temperature. Articles entering the cooling channel after the production is started will be cooled more than desired.
Different embodiment of universal cooling channels are known from the German magazine "Suesswaren" 1/2-1988, pages 43-47. The cooling medium enters the cooling channel in the middle region in a way that at least two cooling stretches are formed. Depending on the relative directions of movement, the articles are cooled in an inverse movement or in the same direction. It is desired to cool the articles carefully in the entering region of the cooling channel to have a positive effect on the aftercrystallization in the chocolate mass. The temperature profile has its minimum approximately in the middle region of the cooling channel. The temperature increases a little bit in the direction toward the exit of the cooling channel to prevent humidity from condensing at the articles.
Certain physical requirements have to be met to successfully cool chocolate covers. It is necessary to provide a careful and gentle cooling effect in the region of the entrance of a cooling channel. The temperature of the cooling medium is comparatively great to exclusively stimulate the increase and the growth, respectively, of the stable Beta V-crystals that have been formed during the precrystalization of the chocolate. When this temperature of the cooling medium at the entrance of the cooling channel decreases due to a low heat load (due to a decreased flow of products and a partial load), the temperature difference between the warmer chocolate cover and the temperature of the cooling medium (air or water) is increased. This has the effect of undesired unstable Beta IV-crystals being formed.
The temperature of the surfaces of the articles exiting the cooling channel preferably is more than, for example, in the middle region of the cooling channel. This temperature preferably is constant, and it has a value such that the surface of the articles does not reach the dew point when the articles reach the packaging region after leaving the cooling channel.
When the dew point is reached humidity condenses on the surfaces of the articles. A small amount of humidity on the product cannot be seen, but it leads to the so-called sugar frost being solved from the chocolate by the humidity. As mentioned above, a low entering temperature results in undesired unstable Beta IV-crystals being formed in the cacao butter. Since cacao butter is polymorph, it may solidify in different forms of crystals (stable and unstable crystals). Only the stable crystals guarantee for a good and permanent gloss. Cacao butter also is monotropic. This means that different forms of crystals may convert independently. This is only true for low melting unstable crystals turning into higher melting stable crystals.
When unstable crystals are formed in the first part of a cooling channel due to a strong cooling effect, the crystals automatically convert into stable crystals after a few weeks. The conversion of the crystals in cacao butter in a chocolate product results in energy being set free, and in the undesired fat frost (gray haze) on the surface of the product.
In the above described cooling channels and similar cooling channels, it is desired to provide a certain temperature profile along the length of the cooling channel by the cooling medium in the at least two cooling stretches. The temperature is higher at the entrance and at the exit of the cooling channel than in the middle region in which it reaches its minimum. Consequently, the region of the entrance of the cooling channel is carefully cooled, the middle region is cooled more powerful, and the temperature of the articles is slightly increased in the region of the exit. In this way, it is ensured that the temperature of the surface of the articles at the exit of the cooling channel is not too low. It is prevented that humidity condenses on the articles. In case such humidity does condense, the durability of the articles being covered with chocolate is reduced, and the articles do not look as good as desired. The articles look dull and gray. After a number of articles have passed the cooling channel in case of a new start of the production and an adaptation to the constant load of the cooling channel has been attained, the cooling channel fulfils its desired function. This means that the articles are correctly cooled, and their surfaces have the desired gloss and firmness as it is necessary for packaging. When no articles enter the cooling channel and the production is stopped, the cooling medium does not absorb heat any more. Consequently, the cooling medium does not heat up either. This means that the final or end temperature of the cooling medium substantially corresponds to the beginning temperature of the cooling medium after a short period of time. The temperature is correspondingly low. When articles do enter the cooling channel afterwards, these articles are cooled to a great extent, and the above described disadvantages occur. The temperature of the cooling medium is too low. This is true at the entrance of the cooling channel as well as at the exit of the cooling channel.